A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal to create an electrical signal with precise frequency. There are several different types of crystal oscillators each having different features relating to frequency management and control.
A crystal oscillator can be used to generate a clock signal that can be used for timing purposes in integrated circuits. The operation of a crystal oscillator can be broken down into two phases: startup and steady-state operation. The time from startup to steady-state operation can be referred to as the startup time of the crystal oscillator.
Crystal oscillator startup times are generally a function load capacitance and feedback gain of the circuits of which the crystal oscillator is a part. High-precision clocks based on crystal oscillators typically have long startup times.
Resistive-capacitive (RC) oscillators generally have a faster startup time than crystal oscillators. However, RC oscillators are generally not as precise as crystal oscillators and the frequency of a signal generated by a RC oscillator tends to be sensitive to changes in voltage, temperature and other effects. Ring oscillators based on inverters can also be used.